1. Field of the Invention
This invention relates to an adhesive composition which adheres strongly to any of hard tissues in a living body, such as teeth and bones, metals, organic polymers and ceramics, and exhibits an adhesive strength which is not easily affected by water. The term "adhesive composition" as herein used not only means a composition used for bonding a plurality of adherends to one another, but also covers a composition used for forming a highly adhesive coating on the surface of an adherend such as a metal or organic polymer, and a composition used for forming a highly adhesive filling material for repairing hard tissues in a living body. In other words, this invention covers any and all compositions that are adhesively applicable to various kinds of substances, including hard tissues in a living body, metals, organic polymers and ceramics.
2. Description of the Prior Art
Various kinds of metals, organic polymers and ceramics are used for the restoration of teeth. When these restorative materials are mounted in the mouth, it is necessary to ensure that they be secured bonded to teeth, or to each other. Since they are placed in the mouth, it is particularly necessary that satisfactory adhesion be obtained in a wet condition. A variety of attempts have hitherto been made to explore a practically useful adhesive for dentistry as will hereinafter be set forth. Although some adhesives have been put to practical use, they are used only for a limited scope of application, since they do not work satisfactorily. If there is developed an adhesive which can strongly bond a metal or organic polymer to a tooth, or a metal to an organic polymer in a wet condition, it is believed to contribute greatly to improving the art of dental restoration. An adhesive which provides a high adhesive strength in a wet condition is also believed to be useful for a lot of other applications.
U.S. Pat. Nos. 4,259,075 and 4,259,117 show that a polymerizable composition containing a vinyl compound having a group of the formula ##STR3## is effective as a dental adhesive. U.S. Pat. No. 4,222,780 shows that a polymerizable composition containing a vinyl compound having a group of the formula ##STR4## is also an effective dental adhesive.
In fact, some of the compositions defined by these patents are widely used as a primer for application to the wall of a tooth cavity before the cavity is filled. They, however, require acid etching of the cavity wall in order to provide a satisfactory adhesive strength for the tooth. Moreover, they do not provide any satisfactory adhesive strength for a Ni--Cr alloy containing 93% Ni and 6% Cr, and used commonly in dentistry.
There have also been proposed dental adhesives prepared from polymerizable phosphate compounds as will hereinafter be described. None of them has, however, been put to practical use because of their unsatisfactory adhesive strength.
(i) U.S. Pat. No. 3,882,600 described phosphoryl monofluoride.
(ii) Journal of Dental Research, vol. 53, pages 878 to 888 and vol. 56, pages 943 to 952, Chemical Abstract, vol. 77, page 290 (66175 g) and Japanese Laid-Open Patent Specification No. 44152/1976 describe CH.sub.2 .dbd.CH--PO(OH).sub.2 and CH.sub.2 .dbd.CHC.sub.6 H.sub.4 CH.sub.2 PO(OH).sub.2.
(iii) Japanese Laid-Open Patent Specification No. 113843/1978 shows by a general formula the compounds obtained by neutralizing one of the two hydroxyl groups in the compounds of the formula ##STR5## in which R stands for an organic residue having at least one vinyl group. More specifically, it shows the following compounds. In the following formulas, M stands for an alkali metal: ##STR6##
None of the compounds set forth at (i) to (iii) above provides a satisfactorily high adhesive strength in a wet condition.
There have also been made a number of other proposals to provide adhesives which are useful for both teeth and metals, as will hereinafter be summarized.
(i) U.S. Pat. No. 4,148,988 shows 4-methacryloxy ethyl trimellitate as an adhesive monomer. This monomer, however, cannot maintain a strong bond between a tooth and a metal or organic polymer for a long time in the mouth in which a wet condition and repeated occlusal pressure prevail.
U.S. Pat. No. 3,872,047 and Japanese Laid-Open Patent Specification No. 98878/1974 disclose a polymer having both a hydrophilic group and a hydrophobic group as an adhesive constituent. They show methacryloxyethyl phosphate as a monomer constituting the polymer. This polymer does, however, not appear to provide any satisfactory adhesive strength.
(iii) It is known that a polymer obtained by polymerizing a vinyl monomer on the tooth surface employing a ternary curing agent composed of a peroxide, an amine and a sulfinate has an improved adhesive strength on the tooth (U.S. Pat. No. 4,182,035). No satisfactory adhesive strength can, however, be obtained from any combination employing a known vinyl monomer, but it is believed necessary to explore a new adhesive vinyl monomer.
It is known that if a polymerizable composition containing 2-(meth)acryloyloxyethyl dihydrogen phosphate is cured on an iron or stainless steel surface, the cured product adheres to the metal surface, as described in the various references which will hereinafter be cited. No attempt has, however, been hitherto made to obtain phosphate esters having a higher adhesive strength than 2-(meth)acryloyloxyethyl dihydrogen phosphate, particularly in a wet condition.
A. U.S. Pat. No. 3,754,972 discloses the formation of an adhesive coating on a metal surface by applying a polymerizable composition containing a phosphate ester thereto. While it shows the applicable phosphate esters by way of a general formula, the examples set forth therein provide a specific support for the adhesive property of only the compounds of the following formula obtained by reacting hydroxyethyl acrylate with P.sub.2 O.sub.5 : ##STR7## in which m is 1 or 2, n is 1 or 2, and m+n=3.
B. U.S. Pat. No. 3,884,864 discloses the manufacture of a phosphorus cured material which is useful as a fire retardant material, and says that it shows a high adhesive strength on a metal. It is, however, manufactured from phosphate esters obtained by reacting hydroxyethyl methacrylate or .beta.-hydroxychloropropyl methacrylate with P.sub.2 O.sub.5. They are the phosphate esters represented by the general formula I which will hereinafter appear, and in which R.sub.2 has a maximum of three carbon atoms.
C. U.S. Pat. No. 3,987,127 discloses a radiation polymerizable coating composition containing a polymerizable phosphate ester. It shows a general formula for the applicable phosphate esters which includes those represented by the formula I when R.sub.2 stands for an alkylene group having a maximum of six carbon atoms. The compounds listed specifically therein, and employed in the examples are, however, only those obtained when R.sub.2 is a group of the formula --CH.sub.2 CH.sub.2 --. It does not give any example of the compounds containing an alkylene group having three or more carbon atoms.
D. U.S. Pat. No. 4,001,150 discloses a composition containing a polymerizable phosphate ester, and used for preparing an electroconductive resin. The applicable phosphate esters shown by way of example therein are those represented by the formula I when R.sub.2 is an alkylene group having a maximum of four carbon atoms. The patent says that it is not advisable to use any compound containing an alkylene group having more than four carbon atoms.
E. U.S. Pat. No. 4,044,044 discloses an anaerobic adhesive composition containing a polymerizable phosphate ester of the general formula: ##STR8## in which R.sub.a stands for H, CH.sub.3 or C.sub.2 H.sub.5, R.sub.b stands for --CH.sub.2 --, --CH.sub.2 --.sub.2, --CH.sub.2 --.sub.3 or ##STR9## and n is an integer of 1 to 10. It does, however, not show any phosphate ester specifically except 2-methacryloyloxyethyl dihydrogen phosphate.
F. Japanese Laid-Open Patent Specification No. 20238/1974 discloses an anaerobic adhesive containing a compound of the general formula ##STR10## in which R stands for H or CH.sub.3, and Z stands for a halogen. It does not show any attempt to use a phosphate ester having a larger number of carbon atoms.
Japanese Laid-Open Patent Specification No. 100596/1975 describes the usefulness of an organic compound having a P--OH group as one of the constituents of an electroconductive composition, and specifically shows by way of example a compound which corresponds to that of the formula I when R.sub.2 stands for --CH.sub.2 CH.sub.2 -- or --CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 --. It, however, fails to show any other compound having a larger number of carbon atoms.
Japanese Laid-Open Patent Specification No. 125182/1976 discloses a curable resin composition suitable for use in coating a metal surface, but which contains only a compound corresponding to that represented by the formula I when R.sub.2 stands for --CH.sub.2 CH.sub.2 -- or ##STR11##
Japanese Laid-Open Patent Specification No. 12995/1978 discloses a low temperature curable resin composition containing a phosphate ester which corresponds to that represented by the formula I when R.sub.2 stands for ##STR12##
Japanese Laid-Open Patent Specification No. 11920/1981 discloses a polymerizable composition containing an epoxy diacrylate and a phosphate ester as a diluent therefor, and having a high adhesive strength on a metal. Although it shows a general formula for the compounds corresponding to those represented by the formula I when R.sub.2 stands for --[CH.sub.2 CH.sub.2 ]--, in which l is from 1 to 10, it specifically shows only a compound obtained when l is 1, and 2-methacryloyloxyethyl dihydrogen phosphate is the only phosphate ester employed in the examples set forth in the specification.
It will be noted from the foregoing that, though there are a lot of prior patents and patent applications disclosing compositions containing polymerizable phosphate esters as hereinabove mentioned at A to F, it is only the compositions containing 2-(meth)acryloyloxyethyl dihydrogen phosphate corresponding to the compounds represented by the formula I when R.sub.2 stands for a group having two carbon atoms that have specifically been found effective as an adhesive, and that all the other similar compounds shown by way of example therein correspond merely to those represented by the formula I when R.sub.2 stands for a group having two to four carbon atoms. Although these patents and patent applications state that the compositions containing those compounds exhibit a high adhesive strength on metals, none of them speaks of the adhesiveness of the compositions in a wet condition, nor do they contemplate the use of those compositions for dental applications.